This invention relates to an improved design of Zero Insertion Force (ZIF) connector for connecting flexible circuit cables to contacts of a Printed Circuit Board.
As used herein Flat Flexible Circuit (FFC) should be construed is including Flexible Printed Circuit (FPC)
Prior art ZIF connectors have three major weaknesses namely over penetration of the contact into the copper conductors of a flexible circuit cable, dependancy upon a backer (stiffener) for alignment of these conductors, and the lack of strain relief for the connection between the conductors and contacts.
In electrical systems, flexible printed circuits (FFC) are employed as electrical cables for interconnecting rows of terminals of printed circuit boards. Often a connector, mounted to one or both ends of the FFC, has typically been used with a set of electrical receptacles or sockets which are designed to receive terminal posts or contact pads on the printed circuit board.
In today""s electronics market, manufacturers are placing emphasis on increasing their product""s reliability and reducing assembly costs to remain competitive. A primary focus of each manufacturer is to reduce the cost and increase the circuit density associated with interconnecting the sub-assemblies and components found within its products. Another emerging focus in today""s electronics market is to pack more electronic functions into smaller packages. This means higher density modules, each requiring multiple high density interconnections to other modules.
Connector manufacturers have not kept pace with today""s market needs. Simply stated, conventional connector technology cannot accommodate today""s high-density requirements. Most existing connectors consist of individual stamped contacts assembled into a molded plastic housing. The physical size required to manufacture an acceptable spring contact eliminates this technology in high-density circuits. For the last thirty years, electronic systems have been designed around conventional connector technology. Connector manufacturers have effectively led this market, and system designers gladly followed, because these connectors satisfied their needs. This cannot continue as significant events are combining to change the role of connectors forever, including a new generation of chips that are driving PC board manufacturers to product boards with conductors which have 0.015xe2x80x3 or less wide contacts on 0.025xe2x80x3 or less centers. These boards must be inter-connected to other modules or to the outside world and will require a high-density connector and interconnect cable.
These key events have led to development of the high-density zero insertion force (ZIF) connector of the present system.
Additionally due to the push towards lower cost FFC (flat flexible cable) and FPC (flexible printed circuits) to PCB (printed circuit board) connector systems, gold over nickel as a plating choice for connector contacts has been out paced by tin/lead. Unfortunately, though cheaper, tin/lead plating develops a non-conductive oxide layer on its surface. Accordingly special connector contact requirements must be met for low voltage/amperage systems. There are three ways to overcome this oxide obstacle to make a good electrical contact:
a) The first is to displace (plow through) the oxide layer using sufficient force and wipe. This is a traditional design, which has been proven for over 30+ years of usage and has industry acceptance and which, when designed and constructed properly, is highly reliable and is a very ergonomic design. However, the high contact force necessary to maintain a gas tight connection physically limits how small the contact (spring) can be made, the minimum wipe movement physically limits how small the connector can be made. The design is also susceptible to fretting, typically has the added part with an associated increased assembly cost of a header or receptacle, and has a low mating cycle life due to wear characteristics;
b) The second is to extrude the soft tin/lead plating through the brittle oxide layer using enormous amounts of contact pressure. This typically does not have the added part and increased assembly cost of a header or receptacle, and does not have very high reliability and resistance to shock, vibration, fretting, etc. Also, the structural integrity of a connector necessary to provide such a high contact force limits the minimum size of the connector, and applies a bending stress on the circuit board; and
c) The third is to accurately pierce the oxide layer into the tin/lead but not to the copper trace/lead (more commonly known as a Zero Insertion Force (ZIF) contact system). In this arrangement there is no need for the added part and increased assembly cost of a header or receptacle, there is a high mating cycle life due to very low wear characteristics, the design is not very susceptible to fretting. Also the connector can be made very small because there is no need to compensate for high internal stresses, or mating connectors. However, the cable trace/lead plating thickness is critical because the piercing depth should pass through the surface oxides and into the tin/lead plating but not into the copper due to the potential of copper oxide growth (this is a common failure), and the cable thickness is critical because even though most of the contacts are designed to accommodate for some fluctuation in it, it still affects the depth of piercing.
It is easy to deduce from the aforementioned contact system comparisons that the ZIF contact system should prevail as ideal. This is confirmed by the popularity of ZIF connectors today. However, the design of this contact system type has not been performed ideally. Current ZIF connectors do not limit the insertion depth of their oxide piercing contact. They rely upon the thickness of the cable being a very specific thickness and very tight connector construction tolerances. These limitations and the manufacturing, quality, and cost problems that are associated with them are not suitable for connector Depth Limited Film Piercing Gas Tight Contact System (DFGTS).
Current strain relieving systems for most, if not all, ZIF FFC/FPC connectors are circuit compression/surface friction based. They are comprised of a wedge of some sort driving itself between a wall of the connector housing (which is in the same plane as, but opposite to the contacts( and the backside of a FFC/FPC. This forces the exposed portion of the cable against the contacts. This is the only strain relieving that occurs during a typical ZIF connector in it mated state. The friction generated through the force of the contact against the cable is the only thing stopping the cable and actuator (wedge) from backing out if pulled or if the system is under vibration.
The alignment mechanism is critical. Traditional ZIF connectors align the cable by means of the cable width. The edge of the cable rides against the inside wall of the connector contact cavity. This provides the positioning of the contacts to the cable traces. It also means that the alignment is only as accurate as the tolerance that can be held. The trace to the cable""s edge is typically +/xe2x88x920.005 inches, the contact to the wall connector-housing wall is +/xe2x88x920.002 inches, which means if all the tolerances are on the high side of a industry standard 0.5 mm ZIF prepared FFC, there could be bridging, and/or cross talk. The ZIF prepared FFC must also have a backer/stiffener added to the backside because, due to the cable""s flexible nature it""s own dielectric world not provide the stiffness required.
It is an object of the present invention to provide a separable connector system for reliably and releasably connecting the conductive circuit paths of a FFC to closely packed (high density) conductive contacts, connected to a PC board in a way that does not require springs, solder, crimping or welding operations in order to inter-connect the two circuits, the connector system providing accurate registration to ensure reliable desired connection.
A further object is to provide a ZIF connector system which can be formed as an inexpensive structure, is relatively easy and inexpensive to make in quantity and can be mounted to the end of a FFC without requiring any tool and which can be readily connected to and aligned with contacts connected to a PC board.
An object of the invention is also to provide a ZIF connector overcoming the inadequacies of the prior art and to provide a design of DFGTS to mechanically limit the insertion depth of the force concentrator while still allowing it a greater range of deflection than standard contact systems introducing the allowance for wider tolerances on FFC and FPC construction.
This is achieved by providing a force concentrator for each contact to which the ZIF connector is to be attached. When a trace (conductor) of a FFC or FPC is applied with minimal force to the DFGTS, the force concentrator will pierce only to its height due to the conductor bottoming out on a surface in the housing, thus making it depth limiting. Due to its ultra simple design it can be optimized for offsetting cable incongruities through deflection because it does not have to be designed to take into account additional deflection requirements to make up for a number of manufacturing tolerances due to an overly complicated shape.
The connector of the present invention does not, in a preferred form, rely on the friction type of strain relieving connection. While is does not provide for displacement motion for the cable it also does not rely on the contacts for frictional locking but rather on the penetration of the force concentrator of the contacts through the dielectric of the FFC or FPC into contact with the conductors of the FFC or FPC. The cable may be planarly displaced by the contacts"" having a cammed portion instead of using piercing. This would still provide a strain relief but would not pierce the dielectric. This would be important for higher voltage applications. In addition, a contact which has a depth limiting contact bump on the lower beam may be provided, this bump can be plated on, scored in etc. It would be used in connection with the deflection strain relieving method. The ZIF connector of the present invention has ribs to align the cable by its inherently stiffest member, the conductors. Since the conductors fall in-between ribs in the connector housing the entire cable is no longer dependent upon the margins tolerance and edge stiffness of the cable, which eases the cable manufacturing, lowers cable cost and eliminates the added expense of the stiffener backing material. There is also a lower tolerance stack up between the alignment of the contacts and the conductors because they are now being directly aligned by the same physical divider means (ribs). This direct contact to conductor alignment also provides the connector with the additional benefit of isolating the connection points giving positive increases in the performance of the electrical contact and its operating parameters.
The connector also provides positive locked, unlocked and lock release states by the use of locking latches on the outer housing which cooperate with openings and ramps (cam surfaces) in the inner housing to provide visual, audible and tactile indication of the connector status.
The ZIF connector of the present invention provides:
i) Depth Limited Film Piercing Gas Tight Contact System;
ii) Integrated Alignment and Planar Displacement Strain Relieving System;
iii) Specialized Actuators True Locking Snaps with Visual, Audible and Tactile Feedback; and
iv) Maintains Competitive Pricing through Design for Easy Manufacturing.
Accordingly the invention provides a zero insertion force (ZIF) connector for connecting a flat flexible cable (FFC) to contacts of a printed circuit board (PCB) comprising a) first and second non-electrically conductive housings which are relatively moveable by a telescopic motion between an unlocked state in which an FFC may be freely inserted into the housings for engagement with the contacts and a locked state in which the conductors of the FFC, when present, are captively engaged in electrical contact with the contacts; and b) a latch system interconnecting the housing to allow telescopic motion of the housings from their unlocked state to their locked state, to retain the housings in their locked state and inhibit separation of housings.
Also provided is a zero insertion force (ZIF) connector for connecting a flat flexible cable (FFC) to contacts of a printed circuit board (PCB) comprising a) first and second non-electrically conductive housings which are relatively moveable by a telescopic motion between an unlocked state in which an FFC may be freely inserted into the housings for engagement with the contacts and a locked state in which the conductors of the FFC, when present, are captively engaged in electrical contact with the contacts; and b) contact and FFC conductor alignment ribs sized and spaced to receive an FFC and to align conductors of the FFC with contacts in the connector for electrical connection of each conductor with an associated contact; wherein the space between each pair of ribs is sized to closely receive a conductor to accurately align the FFC, when present, in the connector and to accurately align the contacts in spaced parallel relationship for alignment with the FFC conductors, when present.
Also provided is a zero insertion force (ZIF) connector for connecting a flat flexible cable (FFC) to contacts of a printed circuit board (PCB) comprising a) first and second non-electrically conductive housings which are relatively moveable by a telescopic motion between an unlocked state in which an FFC may be freely inserted into the housings for engagement with the contacts and a locked state in which the conductors of the FFC, when present, are captively engaged in electrical contact with the contacts; b) a latch system interconnecting the housing to allow telescopic motion of the housings from their unlocked state to their locked state, to retain the housings in their locked state and inhibit separation of housings; and c) contact and FFC conductor alignment ribs sized and spaced to receive an FFC, when an FFC is present, and to align conductors of the FFC with contacts in the connector for electrical connection of each conductor with an associated contact; wherein the space between each pair of ribs is sized to closely receive a conductor to accurately align the FFC, when present, in the connector and to accurately align the contacts in spaced parallel relationship for alignment with the FFC conductors, when present.
Also provided is a method of connecting a flat flexible cable (FFC) with a connector to provide zero insertion force for the FFC, strain relief, and a gas tight electrical connection between conductors of the FFC and electrical contacts of the connector comprising steps of a) providing first and second housings moveable between unlocked and locked states; b) providing a plurality of ribs in the first housing, the ribs defining an entry slot for the FFC and spaces between the ribs to receive and align conductors of the FFC and the contacts; c) providing the contacts with a dielectric penetrating wedge; d) providing an FFC with a connector end having exposed parallel conductors, spaced and sized to fit within and be aligned by the spaces between the ribs, and a dielectric backing supporting the conductors; e) providing a latching system for latching the first and second housings in their unlocked and locked states; f) inserting the connector end of the FFC through the entry slot with the housings in the unlocked state with the conductors of the FFC located by the spaces between the ribs in alignment each with an associated contact; g) moving the housings to their locked state whereby a cam surface causes each dielectric penetrating wedge to penetrate the dielectric into but not through an oxide layer of the underlying conductor just sufficiently to provide good electrical contact with the associated underlying conductor and to provide a gas tight such contact and strain relief for the FFC.